Home Optics Experiments PE-1100 LED and Diodelaser

Keywords:

  • Electroluminescence
  • Semiconductor
  • LED
  • Laser Diode
  • Monochromatic Light
  • Coherence
  • Spatial Intensity Distribution
  • Beam Shaping
  • Cylindrical Lenses

 

Basic experiment

Intended institutions and users:

Physics Laboratory

Engineering department

Electronic department

Biophotonics department

Physics education in Medicine

 

Introduction

How it works ...

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PE-1100 LED and Diodelaser

Educational PE-1100 LED and Diodelaser Kit

Nick Holonyak developed the first practical LED in 1962. When electrically biased in the forward direction an LED is able to emit light through electroluminescence. The colour of the emission depends on the semi conducting material used, and can be near-ultraviolet, visible or infrared. The semi conducting chip is encased in a solid plastic lens, which is much more resistant than the glass envelope of a traditional light bulb or tube. Most typical LEDs are designed to operate with no more than 30-60 mill watts of electrical power. Around 2000, commercial LEDs capable of continuous use at one watt of input power were introduced. Nowadays 10 watt units will be available with efficiencies of 60 lumens per watt. These devices produce light similar to a 50 watt light bulb, and facilitate the use of LEDs for general illumination needs. The typical working lifetime of an LED is ten years, which is much longer than the lifetimes of most other light sources. Robert N. Hall is usually cited as the inventor of the semiconductor laser, but Holonyak was involved in the development as well. In laser diodes, light is generated basically on the same principle like in LEDs. But by especially designed semiconductor material laser operation is achieved rather than spontaneous luminescence. Within this experiment, properties of LEDs and Laser Diodes like current dependency, spectral and beam characteristics are investigated. The polarization state of the light emitted by the diodes is determined and beam shaping experiments are performed.

PE-1100 LED and Diodelaser

PE-1100 LED and Diodelaser. Measuring the spatial intensity distribution

Measuring the spatial intensity distribution

PE-1100 LED and Diodelaser Measuring the spectral distribution

Measuring the spectral distribution

PE-1100 LED and Diodelaser, viw of the spectral emission

In first experiments the angular intensity distribution of the LED and the laser diode are measured. A photodiode is attached to the rotatable arm of a goniometer. The measured photo current is converted into a voltage and measured by the provided digital voltmeter. The light source is placed as close as possible to the pivot point of the goniometer. It will be noted, that the emission of the laser diode has an elliptical beam profile. By rotating the diode laser in the adjustment holder the profile can be measured for both the vertical and horizontal direction.

The subsequent experiments are used to study the spectral emission of the provided light sources. For this, the emitted radiation of the light source illuminates the adjustable slit. The image of the slit is projected by means of the imaging lens to the image screen which is fixed to the goniometer arm. After passing the grating the incident light is divided into multiple orders and the spectral distribution becomes visible as vertical bars (line), the image of the slit. The intensity of the image on the screen depends on the adjusted width of the slit. Closely neighboured lines may merge if the width of the slit is too wide.

 

PE-1100 LED and Diodelaser

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PE-1100 LED and Diodelaser, viw of the spectral emission